The present invention relates to electrical circuits, and more particularly to a system and method for providing an improved charge pump monitor for maintaining a charge pump voltage at a particular voltage.
System designs are routinely constrained by a limited number of available power supply voltages. For example, a portable computer system powered by a conventional battery has a limited power supply voltage. Many components (e.g., non-volatile memory) require power to be supplied at operating voltages of a greater magnitude than the power supply voltage available. Therefore, designs have evolved in power conversion circuitry to efficiently develop the required operating voltages. One such power conversion circuit is known as a charge pump. The demand for highly efficient and reliable charge pump circuits has increased with an increasing number of applications using battery power such as notebook computers, portable telephones, battery backup data storage, remote controls and a variety of portable instrumentation devices.
Inefficiencies in conventional charge pumps lead to reduced system capability and lower system performance in both battery and non-battery operating systems. Inefficiency can adversely affect system capabilities, e.g., limited battery life, excess heat generation, and high operating costs. Charge pump monitor circuits are employed to ensure efficient operation and adequate voltage amplitudes required for charge pump circuits. However, the charge pump monitor circuits also require power, thus reducing the efficiency of the system. Furthermore, the charge pump monitor circuits periodically load the charge pump circuit to determine the amplitude level of the charge pump, so that the charge pump circuit can be efficiently charged to the appropiate voltage level. This periodic loading also has a deleterious effect on the power usage of the system.
FIG. 1 illustrates a prior art system employing a conventional charge pump monitoring system 20. The charge pump monitoring system is electrically coupled to a charge pump 10 and a control system 12. The charge pump monitoring system 20 includes a switch 22, a comparator device 30 and a voltage divider circuit 24. The voltage divider circuit 24 includes a first resistor and a second resistor 28. During normal operation, the control system 12 periodically closes the switch 22, which causes the output of the charge pump 10 to be coupled to the voltage divider circuit 24. The voltage of the charge pump 10 is reduced by the voltage divider, so that it can be input into the comparator device that operates at a reduced voltage (e.g., 5 volts). The reduced voltage is then compared to a reference voltage by the comparator device 30. If the reduced voltage is not at an appropriate level, meaning that the charge pump is not at an appropriate level, a signal is sent to the control system 12 from the comparator device 30. The control system 12 then charges the charge pump 10 until it reaches the appropriate voltage level. Once the charge pump 10 reaches the appropriate level, the switch 22 is opened by the control system 12, thereby disconnecting the monitoring system 20 from the charge pump 10.
The above methodology is repeated continuously so that the charge pump maintains an appropriate amplitude level. However, the voltage divider draws relatively large amounts of current from the charge pump resulting in inefficiencies in the system. Large resistors may be utilized to reduce the current draw, however, large resistors are expensive and impractical in small integrated circuits. In view of the above, it is apparent that there is an unmet need for improvements in charge pump monitors in a system employing a charge pump.
A system and method is provided for monitoring a voltage level of a charge pump device. The system and method employ a first charging device that is coupled to an output of a charge pump through a switching system. The first charging device utilizes a minimal amount of charge from the charge pump device to charge to a first voltage level. The first charging device is then decoupled from the output of the charge pump device and coupled to a second charging device. The charge on the first charging device is then redistributed between the first charging device and the second charging device. The output of the second charging device is at a second or reduced voltage level (e.g., below 5 volts) based on the ratio of the charge distribution between the first and second charging devices. The output of the second charging device can then be compared to a reference voltage to determine if the voltage of the charge pump device is at an appropriate voltage level. If the voltage level of the charge pump device is not at an appropriate voltage level. The charge pump device is charged or discharged as necessary.
In one aspect of the invention, a charge pump monitor circuit is provided utilizing a first capacitor and a second capacitor for reducing the voltage level associated with the charge pump below a 5 volt level. The first capacitor is coupled to an output of a charge pump through a first switch (e.g., a transistor). The first capacitor is selected to be of a relatively small capacitance, such that the first capacitor utilizes a minimal amount of current from the charge pump device to charge the first capacitor to a first voltage level. The first switch is then opened decoupling the first capacitor from the output of the charge pump device. A second switch (e.g., a transistor) is closed coupling the first capacitor to a second capacitor. The charge on the first capacitor is then redistributed between the first capacitor and the second capacitor. The output of the second capacitor is at a second or reduced voltage level or the first voltage level based on the ratio of the charge distribution between the first and second capacitors. The second capacitor is selected to have a higher capacitance than the first capacitor, such that the voltage across the second capacitor is smaller than the voltage across the first capacitor after the charge redistribution. The output of the second capacitor can then be compared to a reference voltage to determine if the voltage of the charge pump device is at an appropriate voltage level. If the voltage level of the charge pump device is not at an appropriate voltage level, the charge pump device is charged up to the appropriate voltage level. Logic circuitry can be employed so that monitoring and sampling of the charge pump device can be invoked periodically based on a clock cycle.
To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed and the present invention is intended to include all such embodiments and their equivalents. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention, when considered in conjunction with the drawings.